This invention relates generally to baghouses and more particularly to top inlet baghouses.
The types of bag fastenings vary depending on where they are made; from above or below the tubesheets. They also vary depending on the type of thimbles; some thimbles are slidable in the holes in the tubesheets and some are welded to the tubesheets.
One current method of securing a bag is to sew a flexible metal band in the bag cuff and to have it bear on an internal thimble bead as in FIG. 3 of U.S. Pat. No. 3,177,636. This approach requires very exacting manufacturing tolerances. The sewn-in snap band has to be a near-perfect fit to match the inside diameter of the upper thimble. Since the bag and thimble are usually manufactured by two different suppliers, there is a high level of quality control required and two sources of error. If one, or both diameters are not correct, the bag may not go in (too big) or it may slide off (too small) or, if it is not a snug fit, it may not be adequately air-tight for the service conditions.
Another type of deficiency relates to costs. A manufactured product that requires a minimum of quality control should cost less than one that requires a maximum of quality control. A design that minimizes field labor costs is preferable to one that does not.
The fastenings described in this disclosure require a minimum of quality control. Because shop labor is less costly than field labor the top fastening in this disclosure is made by the bag manufacturer. Bottom inlet bags are frequently supplied with disposable metal caps. Shop assembly is less costly than field assembly--the labor cost difference may pay for the cap. In addition, bad fits are found and corrected in the shop instead of at the job site.
Sewn-in snap bands are popular because they obviate the need for clamps and for the tools and labor to install the clamps in the field. Another way to avoid clamps, tools and field labor is to have the bag supplier also furnish the thimbles and to attach the bags to the thimbles in the manufacturing shop.
Another method which is utilized is to slide the cuff over an external thimble bead and to use a hose clamp in the space between the rope bead at the end of the bag cuff and the thimble bead.
Bags for existing top inlet baghouse dust collectors are fastened by a variety of means. Often, these fastenings suffer from one or more of the following faults:
1) labor and material for fastenings are too costly, PA1 2) bottom fastening in some designs has to be from below the lower tubesheet--a dirty and hazardous job, PA1 3) divided responsibility for quality control may cause defective fastenings.
There is a significant need for fastenings which do not suffer from any of these limitations.